@dmiller_SCE
Thank you the reply. I understand that the opaque appearance is resulted by the material assigned to the system.
Sending the question to the forum I have had a hope that the community could suggest a workaround. Or an Autodesk representative would find that such appearance works "as designed", but not "as expected".
We really experience problems working with piping system graphics conflicting expected equipment appearance. For example, traditionally a return pipe on single line drawing should be shown with a dash line. Applying this graphics override for the piping system makes mechanical equipment appearing with dash line. Often the equipment is connected to several system and its graphics changes randomly. It is not good.
We are trying to cope with the problem in two ways:
1. Assigning solid line for piping system and applying Filters for view to show return pipes with dashed lines.
2. Assigning dash line for piping system and applying Filters for view to show equipment with solid lines.
A big disadvantage for both methods is that they don't work properly when we need to show "existing" graphic presentation. The problem is that the Filter overrides the phase graphics override.
All that is big pain for us. And now we found the problem with clearance appearance. Quite long ago I came to conclusion that system's graphics override should not affect the Mechanical Equipment category. Maybe a proper solution exists and it can be generously shared on the forum. If not it would be nice if Autodesk take a look for that problem.